万能公式

https://en.wikipedia.org/wiki/Tangent_half-angle_substitution

Various books call this the Weierstrass substitution, after Karl Weierstrass (1815 – 1897), without citing any occurrence of the substitution in Weierstrass' writings,[2][3][4] but the technique appears well before Weierstrass was born, in the work of Leonhard Euler (1707 – 1783).[，

这公式在机械臂运动反解中常用，见过通过构造半角正余弦的证明

分母求错了吧？